Multicolor ITO/SiOx/p-Si/Al Light Emitting Diodes with Improved Emission Efficiency by Small Si Quantum Dots

In this paper, multicolor ITO/SiOx/p-Si/Al light emitting diodes (LEDs) made by Si quantum dot (Si-QD) embedded Si-rich SiOx grown by detuning the radio frequency (RF) plasma power under the plasma-enhanced chemical vapor deposition system are presented. With the Si-QD size shrinkage obtained by increasing the RF plasma powers from 30 to 70 W, the turn-on voltage of red, green, and blue ITO/SiOx/pSi/Al LEDs is found to increase from 70 to 99 V, with the maximum electroluminescent power increasing from 9 to 423 nW. The corresponding power-current slope and power conversion ratio are observed to greatly increase from 0.6 to 28 mW/A and from 8 x 10(-6) to 2.4 x 10(-4), respectively. The power-current conversion ratio of the ITO/SiOx/p-Si/Al LEDs increased with decreasing Si-QD size, indicating that the carrier recombination rate is much higher in the smaller Si-QDs, which was corroborated with the carrier lifetime analysis. On the contrary, the carrier accumulation results of the multicolor ITO/SiOx/pSi/Al LEDs obtained by using C-V hysteresis analysis show the opposite trend to that of the power-current conversion ratio. It is observed that the bigger Si-QDs exhibit a higher capability for carrier storage and the charge loss rate is degraded by two orders of magnitude when the Si-QD size shrinks from 4.1 (largest) to 1.8 (smallest) nm.